Rotating lead screws or threaded members are often used to locate a threaded element within a machine. In many applications, movement of the threaded element relative to the lead screw must be done accurately, repeatedly and with a relatively constant drag force in both a forward and reverse direction. Typical applications include data printers, x-y tables used as peripheral equipment in the computer industry, and loading mechanisms in copiers.
There have been many attempts to design anti-backlash nuts for meeting the tolerance requirements in precision equipment. A prior attempt is shown in U.S. Pat. No. 3,656,358 which discloses a linear positioning device having an improved collar. The collar is telescoped over and adapted to be translated relative to an elongate threaded rod. The collar includes cantilevered fingers resilently wedged into spaced grooves to preload the collar onto the rod and prevent rotational play.
U.S. Pat. No. 3,997,269 discloses a self-aligning anti-backlash nut having a tubular nut body which co-acts with a concentric spring sleeves. Generally, the nut body includes a pair of spring biased elements provided with internal threads adapted to engage the external threads of a screw. In a preferred embodiment, a self-aligning spring sleeve has three pairs of oppositely disposed transverse slots to obtain the desired alignment characteristics. The nut body includes a base portion separated from the spring bias elements by two transverse slots which cooperate with an adjacent pair of slots in a spring sleeve to form a universal joint. A remaining slot pair in the sleeve is oriented circumferentially with respect to the first pair by an angle of 90.degree. with a third pair of slots being circumferentially aligned with the first pair.
U.S. Pat. No. 4,249,426, (U.S. Pat. No. Re. 32,433) discloses an anti-backlash nut having one or more longitudinal flexural members with one end fixed and one end free floating. The flexural members include ramps on the free floating ends and an axially compressed spring is used to apply an axial force on the ramps and thereby create a radial force vector which maintains the ramps in contact with the threaded shaft.
However, each of the prior anti-backlash nuts provides a relatively small thread engagement area, approximately two to three threads, with the threaded lead screw. As the thread engagement area is limited, the rate of wear is accelerated. Therefore, almost any wear has a very detrimental effect on performance of the component. That is, many of the prior anti-backlash nuts have very little tolerance to wear.
Alternatively, anti-backlash nuts may be individually produced by creating precision threads. The precision threads identically match the threads of the lead screw to provide accurate tracking of the threaded member. However, the cost and quantity of precision thread manufacture is incompatible with the cost requirements of mass produced machines.
Therefore, a need exists for cost competitive anti-backlash nut having improved wear characteristics and tolerances. The need also exists for an anti-backlash nut having a size which is compatible with a variety of applications and which provides an increased thread engagement area between the anti-backlash nut and the threaded shaft. A further need exists for an anti-backlash nut which can be reliably mass produced without requiring extensive machining of the component parts.